The present invention relates to a method of mixing a hot furnace gas with another gas before the hot furnace gas is removed from the furnace by directing the hot furnace gases out via a hood which forms an uninterrrupted space for gas with the furnace space. The invention also relates to a cylindrical hood, intended for use in connection whith this method, the open end of the hood adjoining the gas space of the furnace and the hood having an outlet pipe for the hot gases treated in a controlled manner in the hood.
The invention relates in particular to a method of smelting and reducing raw material in a furnace, e.g. a method for smelting and reducing ferrosilicon or silicon in an electric-arc furnace, be feeding a reductant and the raw material to be reduced into the furnace and by removing the reduced material in the form of a melt from the bottom of the furnace and by removing the hot gases from a reducing-gas space above the melt by using a downwards open hood fitted on top of the electric-arc furnace, the hood having in its cover openings for electrodes and an outlet pipe for the gases and feed inlets for the raw material to be smelted and reduced and for the reductant.
It would often be desirable to reduce, oxidize or cool immediately the hot furnace gases emerging from the furnace, before they are discharged from the furnace gas space. The immediate oxidation, reduction or cooling of hot furnace gases has, however, proven to be very difficult because hot furnace gases have, as is well known, a very high viscosity. In addition, it would often be desirable to separate at least part of the dusts present in the hot flue gases, in order to return the dusts to the furnace before the hot furnace gases are discharged from the gas space of the furnace. As regards the hot furnace gases which contain combustible constituents, it would be especially desirable to burn these combustible constituents before directing the hot furnace gases out of the furnace gas space, so that the heat of combustion could be exploited to as high a degree as possible in the furnace itself. For this reason it would be especially important to be able to mix combustion air with such hot gases, which contain reducing constituents, already in connection with the furnace space itself in order to burn these gases in a controlled manner so that no overheating can occur and that the heat is at the same time recovered indirectly.
Previously known are various furnaces provided with hoods, in which the gases are led directly into the outside air or, after the treatment of the gas, into the outside air. These furnaces have a disadvantage in that the combustion air comes into contact with the furnace gas and the feed bed in an uncontrolled manner.
Previously known are various so-called semi-closed furnaces, i.e., the furnace is provided with a hood. The hood wall has openings provided with hatches. They have a disadvantage in that, for example, the hatch of some opening is open for the pick device of a ferrosilicon or silicon furnace, thereby causing air to come into contact with the furnace gas and the feed bed in an uncontrolled manner. This causes the following disadvantages: investments must be made in oversized gas treatment systems subsequent to the furnace, reductants present in the feed bed are wasted, furnace gases burn in an uncontrolled manned, thereby causing overheating and damage to the hood and electrodes or to other devices.
In order to eliminate the above disadvantages, there has now been provided a method and device by means of which the furnace gases can be treated in a controlled manner.